The present invention relates to a method for carrying out a reactor internal and, more particularly, to a method for carrying out a reactor internal suitable for carrying out a core shroud in a reactor pressure vessel (hereinafter referred to as an RPV) in a boiling water reactor nuclear power plant (hereinafter referred to as a BWR plant).
In the BWR plant, a nuclear reactor has a core disposed in the RPV. A plurality of fuel assemblies including nuclear fuel material are loaded in the core, and an annular core shroud provided in the RPV surrounds the core. In the BWR plant, operation of the BWR plant is periodically shut down for maintenance and inspection. The core shroud, which is a reactor internal, is also is an object of the maintenance and inspection. If damage such as a crack is found in the core shroud or if replacement of the core shroud is desired from the viewpoint of preventive maintenance, the core shroud in the RPV is replaced to a new core shroud.
Japanese Patent Laid-open No. 8-240693 states one way to carry an existing core shroud out of a RPV to replace with a new core shroud. In the method for carrying out a core shroud disclosed in Japanese Patent Laid-open No. 8-240693, the core shroud is coarsely cut up in the RPV filled with cooling water, these cut pieces are further cut up into finer pieces in a reactor well filled with the cooling water, then, the fine pieces are packed into a container, and this container is carried out. However, the method for carrying out the core shroud disclosed in Japanese Patent Laid-open No. 8-240693 requires two steps of coarse cutting and fine cutting of the core shroud, and takes long time to carry out the core shroud.
Methods for carrying out a core shroud to solve this problem are described in Japanese Patent Laid-open No. 2000-46983 and WO 00/60607. These methods for carrying out a core shroud deal with a core shroud inside a RPV in a BWR plant.
In Japanese Patent Laid-open No. 2000-46983, a cut core shroud is, without being cut up into small pieces, carried out through an opening portion formed in a ceiling of a reactor building by using a crane. This method for carrying out the core shroud will be more precisely explained. After operation of the reactor was shut down, a top head of the RPV is removed and a steam dryer and a stream separator in the RPV are taken out from the RPV into an equipment pool. Furthermore, fuel assemblies in the core are taken out into a fuel storage pool. The core shroud is cut below a core plate, and surrounded by a cask which is a radiation shield. The cask storing the core shroud is lifted by the crane, and carried out of the reactor building through the opening portion formed in the ceiling of the reactor building. Afterward, a new core shroud hoisted by the crane is carried inside the reactor building through the opening portion in the ceiling, and disposed to a predetermined position in the RPV.
WO 00/60607 also states a method for carrying out a core shroud in which method, a core shroud cut below a core plate and surrounded by a radiation shield is carried out of a reactor building through an opening portion formed in a ceiling of a reactor building. In this carry method, various parts such as removed jet pumps and cut pipes to be carried out are stored inside the core shroud above the core plate disposed in the core shroud, and the core shroud along with these parts are carried out of the reactor building.
Japanese Patent Laid-open No. 2002-131483 discloses a carry method in which a reactor including a core shroud is hoisted by a crane and carried out of a reactor building through an opening portion formed in a ceiling of the reactor building. In this method for carrying out a reactor, a protection device is disposed inside a reactor well to prevent the upset of the reactor being carried out of the reactor building to the fuel storage pool side, and the reactor is carried out through the protection device.